1. Technical Field
The present invention relates to an epoxy resin composition for a printed circuit board, an insulating film, a prepreg, and a multilayer printed circuit board.
2. Description of the Related Art
With the development of electronic devices and request for complicated functions, a printed circuit board has continuously been requested to have a low weight, a thin thickness, and a small size day by day. In order to satisfy these requests, wirings of the printed circuit board becomes more complex, further densified, and higher functioned. In addition, in the printed circuit board, a buildup layer is multilayered, and thus miniature and high densification of wirings are requested. These electrical, thermal, and mechanical characteristics requested for the printed circuit board act as more important factors.
The printed circuit board is mainly composed of copper for circuit wirings and polymer for interlayer insulation. As compared with copper, the polymer constituting an insulating layer requests several characteristics such as coefficient of thermal expansion, glass transition temperature, thickness uniformity, and the like. Particularly, the insulating layer needs to be formed to have a smaller thickness.
As the circuit board is thinner, the board per se has lower rigidity, and thus, may be defective since it is bent at the time of mounting parts at a high temperature. For this reason, thermal expansion characteristics and heat resistance of a thermo-hardening polymer resin are important factors, and the structure of the polymer, the network among chains of the polymer resin constituting the board composition, and hardening density closely affect them at the time of thermal hardening.
Patent Document 1 discloses an epoxy resin composition containing a liquid crystal oligomer. However, the network between a hardener and a polymer resin is not sufficiently formed, and thus, does not sufficiently lower the coefficient of thermal expansion to a level appropriate for the printed circuit board and does not sufficiently raise the glass transition temperature.
Patent Document 1: Korean Patent Laid-Open Publication No. 2011-0108198